This invention relates generally to an electrostatographic printing machine, and more particularly concerns an improved cross-mixer for use in the development system employed therein.
In the process of electrostatographic printing, electrostatic charge patterns are formed and reproduced in viewable form. The field of electrostatography includes electrophotography and electrography. Electrophotography employs a photosensitive medium to form, with the aid of electromagnetic radiation, the electrostatic latent charge pattern. Electrography utilizes an insulating medium to form, without the aid of electromagnetic radiation, the electrostatic latent charge pattern. Development, which is the act of rendering an electrostatic latent image or pattern visible, is employed in all of the aforementioned types of electrostatographic printing. Hereinafter, an electrophotographic printing machine will be described as the illustrative embodiment having the features of the present invention incorporated therein.
An electrophotographic printing machine employs a phooconductive member which is charged to a substantially uniform potential so as to sensitize the surface thereof. The charged portion of the photoconductive member is exposed to a light image of an original document being reproduced. As a consequence of the exposure, the charge is selectively dissipated in the irradiated areas in accordance with the light intensity reaching the surface thereof. This records an electrostatic latent image on the photoconductive surface. Development of the electrostatic latent image recorded on the photoconductive surface is achieved by bringing a developer mix adjacent thereto. A typical developer mix comprises dyed or colored plastic particles, known in the art as toner particles, which are mixed with coarser carrier granules, such as ferromagnetic granules. In general, the toner particles are heat-settable. The toner particles and carrier granules are selected so that the toner particles have the appropriate charge relative to the electrostatic latent image recorded on the photoconductive surface. Thus, when the developer mix is adjacent to the photoconductive surface, the greater attractive force of the latent image recorded thereon causes some of the toner particles to transfer from the carrier granules and adhere thereto. This concept was originally disclosed by Carlson in U.S. Pat. No. 2,297,691 and is further amplified and described by many related patents in the art.
In electrophotographic printing, excessive developer mix is positioned adjacent the electrostatic latent image. The unused developer mix and denuded carrier granules are returned to the sump thereof for subsequent reuse. Mixing of the unused developer mix and denuded carrier granules with new toner particles is promoted by cross-mixing the foregoing with one another. This insures that the triboelectric characteristics will be satisfied. Various types of mixing devices have been developed. For example, structured baffle plates are frequently used when passive cross-mixing is desired. Alternatively, active cross-mixers such as auger systems may be employed to maintain a more or less uniform distribution of the toner particles throughout the developer mix. In this way, the developer mix may be recirculated numerous times without a marked reduction in the quality of the copies being reproduced.
Accordingly, it is a primary object of the present invention to improve active cross-mixers employed in the development system of electrophotographic printing machine.